The brilliant swallowtail butterfly

The brilliant swallowtail butterfly


Posted 8th May 2018


Mid-summer on the Norfolk Broads, at the least on sunny days, will see swallowtails flitting over reed, sedge and fen, along with wetland flowers, hemp agrimony, loosestrife, ragged robin and marsh orchid, brightening up the edges of even the most secluded paths

The swallowtail is the largest and one of the UK’s most localised butterflies, with its beauty certainly making it worth waiting for. Their small dark chrysalises overwinter in the reedbeds, waiting for the temperature to be just right. At this point, adults emerge and dry their wings in the safety of the vegetation prior to taking flight. Adult butterflies will feed on all species of flower before taking flight, with adult butterflies feeding on all species of flowers, but preferring yellow and purple varieties, so will often be found on red campion and yellow iris.

When mated, the females lay their eggs singly on the leaves of milk parsley, and a few weeks later, the small, blackish caterpillars will start to emerge to feed on the host plant. The large, fully formed caterpillars make an impressive sight, with bulging horns to frighten off predators. If they feel threatened, two horn-like bright orange scent glands will emerge from the back of the caterpillar's head, producing a smell which has been likened to pineapple. The swallow-like tails of the swallowtail butterfly (hence its name) play a key part in ensuring its survival, mimicking antennae. These, accompanied by the two red and blue 'false eyes' will confuse predators into thinking they're dealing with a two-headed butterfly.

How to do it

Before visiting, ensure you know how to identify milk parsley - this is the food plant of the caterpillar. Check any plants you see, with the impressive green and black stripy caterpillar potentially being hidden away amongst the leaves. It's best to opt for a still, warm day, and make sure you remember your binoculars. Swallowtails are very fast flying, and don't sit still very often.

If you can't get to the special places listed below...

On rare occasions, migrant swallowtails have arrived from the continent, and in 2014, were spotted hatching in Sussex. These continental arrivals prefer downland, where they will lay their eggs on wild carrot. It's therefore worth keeping your eyes peeled along the south coast - you never know, you may just spot a rare European wanderer.

Special spots

The British race of the swallowtail butterfly is limited to the Norfolk Broads, with sites being chosen which have a vigorous growth of milk parsley, where it will lay eggs on the tallest plants. Although a rare British insect, if you visit one of the special sites on a windless day, from late May to mid-July, you may just be in luck.

Hickling Broad should be your first port of call, with marsh harriers, bearded tits and the common crane all being other potential sights you can add to your list of wonderful sights. Alternatively, try Ranworth Broad - you may even get to spot a swallowtail before leaving the car park!

Norfolk, Upton Broad and Marshes 

Norfolk, Alderfen Broad 

Norfolk, Barton Broad

Norfolk, Cockshoot Broad

Text and information courtesy of The Wildlife Trusts / image courtesy of © Brian Francis





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